The present invention relates to electrochromic devices and more particularly relates to solid-state, inorganic thin film devices.
Electrochromic materials and devices have been developed as an alternative to passive coating materials for light and heat management in building and vehicle windows. In contrast to passive coating materials, electrochromic devices employ materials capable of reversibly altering their optical properties following electrochemical oxidation and reduction in response to an applied potential. The optical modulation is the result of the simultaneous insertion and extraction of electrons and charge compensating ions in the electrochemical material lattice.
In general, electrochromic devices have a composite structure through which the transmittance of light can be modulated. FIG. 1 illustrates a typical five layer solid-state electrochromic device in cross-section having the five following superimposed layers: an electrochromic electrode layer (“EC”) 14 which produces a change in absorption or reflection upon oxidation or reduction; an ion conductor layer (“IC”) 13 which functionally replaces an electrolyte, allowing the passage of ions while blocking electronic current; a counter electrode layer (“CE”) 12 which serves as a storage layer for ions when the device is in the bleached or clear state; and two transparent conductive layers (“TCLs”) 11 and 15 which serve to apply an electrical potential to the electrochromic device. Each of the aforementioned layers are typically applied sequentially on a substrate 16. Such devices typically suffer from intrinsic electronic leakage (between the electrochromic stack layers) and electronic breakdown.
Typically, electrical power is distributed to the electrochromic device through busbars. FIG. 2 illustrates the electrochromic device of FIG. 1, in cross-section, having power supplied from two conductive elements, such as busbars 18 and 19. In order to prevent the busbars from shorting together, the busbars are electrically isolated from one another. Conventionally, this is done by scribing the TCLs 11 and 15. As shown in FIG. 2, the first (lower) TCL 15 is scribed at point P1, making the lower TCL 15 a discontinuous layer, and thereby preventing the busbars from shorting across the lower TCL 15. Similarly, the second (upper) TCL 11 is scribed at point P3, making the upper TCL 11 also discontinuous, and thereby preventing the busbars from being shorted together across the upper TCL 11.
In order to produce electrochromic devices in a more cost effective manner, it is necessary to modify the deposition process to provide for higher yields and to be more amenable to mass production. In general, the yield can be considered to be reduced every time a substrate or other workpiece is cycled between vacuum and atmosphere and vice versa. This is because dust and debris from the coating process—which is inevitably present in sputtering—is ‘blown’ around during venting and pumpdown, and can find its way onto the active layers, leading to defects in the film structure. Ideally, all the layers could be deposited in one single continuous vacuum step, i.e., one coating machine. However, depositing all the layers in a single vacuum step, would require including a laser scribe (or cut of some type) between the deposition of the lower transparent conductor and the deposition of the second transparent conductor in a vacuum system. Such cutting processes are very difficult in a vacuum system. For instance, with regard to laser scribing, it is necessary to maintain an extremely tight focus for the laser. Such focus is very difficult to achieve efficiently with the mechanical tolerances present in the system.
Furthermore, in order for a solid state electrochromic device to function correctly, it is necessary to block electric current from passing between the busbars of the electrochromic device directly, other than through the desired electrochromic mechanism. Any electronic current that leaks or passes through either of the conductive layers serves to short out the required voltage and inhibits the flow of ions through the electrochromic device. As such, leakage current due to intrinsic electronic leakage leads to compromises in device performance including a lowered dynamic range, non-uniform coloration, decreased ionic conductance, slower switching rates, and increased power consumption. Merely increasing the thickness of the ion conductor layer may result in a reduction of leakage current, but at the expense of degraded optical properties, increased layer deposition time and cost, and reduced switching rates. Accordingly, it is desirable to reduce the amount of electronic leakage through an electrochromic device without resorting to a thick ion conductor layer so as to avoid these compromises in performance.